Sheet metal shrinker



K. H. BALL SHEET METAL SHRINKER Jan. 22, 1963 Filed Jul 22, 1958 2 Sheets-Sheet l Jan. 22, 1963 K. H. BALL. 3,075,063

SHEET METAL SHRINKER Filed Jilly 22, 1958 2 Sheets-Sheet 2 flin b; ij'l ttes 3,ttl5,tl68 SHEET METAL SHRINKER Kenneth H. Bail, Los Angeles, tl'aiii, assignor to Douglas Aircraft Company, Inc, hanta Monica, Galif. Filed Italy 22, 1958, Ser. No. 750,140 12 Ctnims. (El. are- 49 This invention relates to sheet metal and is particularly concerned with sheets that, as received from the rolling mill, incorporate snap-buckles within the area of the sheet. These snap-buckles are localized areas of residual stress left by unbalanced thermal or unbalanced mechanical stresses in forming the sheets in the rolling mill and their stress-field is that of radial compression directed toward the center of the buckle. In the sheet-metal working art these snap-buckles are universally designated as oil-cans, a distinguished from the precise metallurgical term, snap-buckles. Accordingly, hereinafter they will b referred to as oil-cans.

The latter consist of localized, flexible areas which, like the bottoms of oil-cans, are so unstable that they can be snapped back and forth out of the plane of the remainder of the sheet. These areas detract seriously from the usability of such sheets for fabricating sheetmetal articles and are believed to be caused primarily by rolling mill thermal or mechanical faults that leave residual stresses in certain locations on the sheet. These stresses usually take the form of radially outwardly directed forces acting outwardly from the central portion of the area, placing this area under a pre-stress that is not in stable equilibrium.

Subject invention provides methods and means for removing these residual stresses by a metal-shrinking action in an apparatus of an improved nature. It is applicable to all types of metals but finds its greatest utility in shrinking aluminum alloy and titanium alloy sheets.

Briefly, this novel shrinking involves the primary step of peripherally clamping the oil can area with mating pressure-rings arranged respectively in clamping contact with the upper and the lower faces of the sheet; heating the rings and the concerned area of the sheet to a'predetermined temperature dependent upon the composition of the sheet; and thereafter applying to the heated oilcan area, a compression force of such magnitude, direction and duration as to remove or neutralize the aforesaid residual stresses.

One type of apparatus contemplated by the invention for performing the method of the present concepts essentially consists of a machine generally of the arbor-press type but modified, among other respects, to convert the plunger member of the press into a two-phase ram cooperative wtih a complementary platen, the ram and platen being adapted to engage the oil-can area with an initial, pre-pressure clamping action that prevents the metal outside the clamp, and not oil-canned, from being affected by the subsequent shrinking operations. The ram and platen each carries a shrinking die in the center thereof, the dies being complementary. These dies are arranged in pairs that are complementarily shaped to suit the particular shape and area of oil-can to be dealt with, as well as its hardness. In the second phase of operation of the ram, which is in two vertically spaced halves united by acornpresison spring, with the periphery of the ram clamping the periphery of the oil can to the periphery of the platen to prevent affecting the metal lying outside the ram-platen unit, a shrinking force is applied to urge the ram and platen still more tightly together. The upper die being axially mo-vably mounted in the lower half of the ram, this action causes the complementary dies to apply to the clamped oil-can a combined compressive and shrinking force sutficient to urge metal away from its center toward. its periphery, thereby to neutraliz the outwardly directed stresses in the oil can that originally caused its distortion. The oilcan area is thus freed of residual stresses and remains permanently in coplanarity with the remainder of the sheet, and will not locally flex.

It is preferred, especially in the case of hard alloy sheets, such as those of titanium, to apply balanced heat concurrently to both faces of the oil-can and to these and other ends, both the ram and the platen incorporate heating means, such as electric resistance heaters embedded therein.

Although the invention contemplates that other forms of apparatus are equally suitable for carrying out the present method, the aforementioned form is, by way of example, shown in the accompanying drawings and will be described hereinafter in conjunction therewith.

In these drawings, FIGURE 1 is a perspective view of said apparatus in the initial, pre-pressure, or clamping stage before the final-pressure lever has been swung for- Wardly;

FIGURE 2 is a detailed perspective view, partly in section, of the mechanism for applying the final, or shrinking, pressure to the oil-can and releasing same;

FIGURE 3 is avertical, substantially central section of the ram-head group, the platen group and the die group, taken on line 33 of FIGURE 1, with the ram in the initial-pressure position;

FIGURE 4 is a similar view of the same parts in the final-pressure, or sheet-shrinking, position thereof;

FIGURE 5 i a vertical, substantially central View of a second species of the shrinking dies, with the curvatures of same and of the oil-can greatly exaggerated, and d FIGURE 6 is a similar View of a third species of the res.

In order to cary out the present method, the machine depicted in the drawings comprises a frame 12 generally of C-conformation and having an upright arm 13 surmounting a platform 14. In the outer, upper end of the C-frame there is formed a hollow, upright guide, hearing, or supporting, collar 15 for slidably receiving a novel ram-unit i7 coaxially mounted therein for movement upwardly and downwardly.

In the conventional manner, the ram-unit includes a cylindrical shaft 16 having mounted thereon a rack 21 adapted for operation by a pinion 23 carried adjacent thereto on a shaft 25} extending horizontally through member 15. At one end, shaft bears a hand-wheel 22 operable to apply the initial clamping pressure, or prepressure, to the oil can area. At its opposite end-portion shaft 20 bears a group 19 of elements arranged and adapted to force the dies to apply the final pressure to the, preferably, heated oil can. In much the customary manner, this group 19 includes an adjustable length lever 24 rotatably mounted on shaft 20, the lower end of lever 24 bearing a counterweight 25 for facilitating clockwise viewing it from the left hand side of FIG. 2 movement of lever 24, as viewed from the left in FIGURE 1, upon exerting the final, or shrinking, pressure upon the clamped oil can area. A ratchet gear member 27 is fixed to shaft 2% adjacent lever 24. The sleeve 26, provided for enabling adjustment of the effective length of lever 24, carries a spring-loaded pawl 29 for engaging it with member 27. A pawl-controlling pin 30 protrude lateraliy from a slot 32 in the pawl-bearing sleeve 26 and seats and unseats with respect to a cam groove 34 in a collar 33 which is rotatively carried by member 15 and surrounding shaft Zft for use in enlarging or diminishing the maximum arc of travel of lever 24 from its position of rest. When collar 33 is moved back into the plane of the paper, as it were, in FIGURE 2, the beginning point of the arc is spaced back far, providing a greater clamping ring 65.

arc of 'travel; and vice'versa. When the pin leaves the groove 34, the pawl is urged forwardly, or clockwise in FIGURE 2, against the ratchet, thus rotating the shaft clockwise and urging the ram forcefully downwardly on its final. pressure stroke. 2

Considering the ram unit in detail, it comprises, ,as shown inFIGURES 3, and 4, two vertically spaced cylindric portions and 37 cooperatively engaged by a coiled spring 38, the two portions 35 and. 37.beingjcoaxially slidable on a central cylindric member 43 mounted coaxially in bores 42 centrally traversing members '35 and 37. Two sets of vertically separated insulating discs, as of micarta, 39 and 40, are provided in member'35, chiefly for the purpose of preventing the transmission of heat to the hand wheel 22 via the'intermediate metallic structure.

The cylindric member 43 is substantially hollow, hearing two parallel laterally spaced, vertical bores, as shown, in each of which is mounted an electric resistance heater 41, which may well be of the well-known fchromalox type, to each of which electric leads 46 are connected, thermocouple 51 and leads 51A being also provided, as shown. A cylindric socket 45 is provided in the upper end of member 35 for enabling union of the ram unit i with the rack-bearing press rod or shaft 16. The lower end-portion of member 43 incorporates radialbores 47 for receiving removable stop pins 48 provided to prevent separation of members 37 and 43 when in use. Die 50 includes a relief groove 52 for breaking the' suction 'action of the die with its socket in order to facilitate the removalof the die. i

The lower end-portion of member 43bears a central bore in which compressive shrinking die 50*ismounted.

The upper die, 50, in this species has a convex working face, as shown, in order to enable it and die 57 to apply to the rather small oil can shown in the sheet of rather soft alloy, a high unit loadsutficient to reduce the upwardly humped oil can to coplanarity with the remainder of the sheet.

The platen 53 has a socket in its upper portion that is coaxial with the aforesaid central bore. In the socket is seated the shanked die 57 having a planar working face, as shown, adapted to cooperate with the convex- 57, thereby "to facilitate the removal of'the, die 49. "A layer of insulating material, 63,- such as Micarta, .or the like, is interposed between the bottomv of the cylindric platen and the platform 14.

It will be comprehended that the ram group terminates,

' at its lower end, iri-anannular face 64 which in effect constitutes a clamping ring and that the cylindric platen member terminates, at its upper end, in a complementary The two rings, on. application of the pre-pressu-re, seize the peripheral portion of? the oil 'can tightly and stably enough to, in effect, segregate the oil can from the remainder of the sheet, so that, upon application of the dies, metal cannot be pulled from or .pushed? to the regions of the sheet that lie outside the rings. For, such woulditself be likely to setup new residual stresses in the aforesaid regions.

Because of the convexity of the working face of the die 50, its pressure is concentrated in the central region there- 1 of, thus causing it to apply a high unit load to the sheet. Such is desirable or permissiblefor heated isoft alloy sheets. 7

In FIGURE 5,-theinventi-orr comprehends a set of dies,

- 71 and 49, so shaped and configured as to deal with the shrinking of the harder alloys, such as aluminum 75 ST alloy and titanium alloys. Die 71 has, as shown, a concave working face adapted toprovide (1) smaller unit loading and (2) a,veftically-,relativelylarge space between the dies into which the forces generated at the peripheral margin of the die-combination are adapted to act in such manner as to urge the heated metal thereat radially outwardly and away from the center of the die combination, thereby to neutralize the stresses that originally set up the oil can. Since this type of hard'alloy sheet, 70, 70A, can withstand considerable direct compression without ringing, this 'die-set is well adapted for shrinking such sheets. Further, the Transite base 62 being resilient to an extent, will yield and prevent deep ringing of softer alloys. The concavity of the upper die enhances the desirability of this species in that the entire upper surface of the oil-can is continuously in contact with this concave surfacefrorn the inception of the shrinking operation, enabling the greater amount of heat-transfer necessary in dealing with the :harder alloys. Obviously, also, a larger area oil cancan be dealt with than in FIG- URES 1-4, inclusive.

Where the sheetis composedof an alloy that is of nearly extreme hardness, a set of dies, 72 and 49, as shown in FIGURE 6, is employed. Both these dies are planar on their working faces so that the unit load exerted thereby on the sheetis lower than in thecaseof the other two sets of dies aforedescribed. Consequently, there is .a

reduction of. the danger of -Brinelling of the oil can while it is being shrunk. Incidentally, the two .planar face dies. of FIGURE 6 may, if necessary, be employed, after the sheet has been processed by means of the-dies of FIGURES. 1-5, inclusive, as finishing dies. That is, any slight ringingJF-or other imperfections in the surface of the sheet remaining after the aforesaid processing may be smoothedout by means of the dies of. FIGURE 6.

The final pressure exerted by means of the lever 24 may be varied to apply different magnitudes of pressure according to the thickness of the sheet and its hardness. To this end, it is only necessaryto vary the angular position of the collar 33 on the shaft 20, thereby to correspondingly vary the arc oftravel of the lever 24 in applying this final pressure.

'It will be apparent to those skilled in the art that various changes and. modifications may bemade inthe construction set forth withoutdeparting from thespirit of the invention, and it is intended that all such changes and modifications shall be embraced within the scope of the subjoined claims.

I claim: 1. A methodofeliminatingan oil-can in metallic sheetmaterial, comprising: supporting said sheet in an operations zone in an attitude in which both faces of the oilcan are rectangularly accessible clamping the peripheral marginal portion of theoil-can in a substantially immobile condition, leaving the remainder .of the oil can relatively mobile;.heating the oil-can while the marginal periphery thereof is clamped; and balancedly applying to-the area of the oil-can that lies radially, inwardly of the aforesaid clamped portion a compression force directed rectangularly to the faces of the sheet and of such magnitude as to produce aneifective resultant vector directed radially outwardly and downwardly with respect to the radially inwardly acting residual forces causing the oil can.

.- 2. A method of eradicating an oil-can in a sheet of metallic material, comprising: supporting thesheet in an attitude in which both facesof the oil-can are approachable towardsJt-he faces; applying an oil-can segregating clamping action to the peripheral marginal portion of the oil-can so as to in effect segregate the metal of the oil can from the remainder of the sheet; heating the oil-can while the peripheral marginthereof is clamped; and applying substantially rectangularly to the faces of the oil can within the periphery thereof a compressive action urging the metal in the free portion of the oil'can radial- .-of metallicv material, comprising: supporting said .sheet in an operations 'zone in an attitude in which both faces of the oil can are accessible from a direction extending substantially rectangularly to said faces; clamping the peripheral marginal portion of the oil-can in a substantially immobile condition so as to leave the remainder of the oil can relatively free; heating the oil-can while the peripheral margin thereof is clamped; and applying rectangularly to the opposite faces of the free portion of said oil-can compressive forces directed to urge the metal in the free portion outwardly toward the periphery thereof, thereby to neutralize the radially directed residual stresses in said oil can.

4. In a machine for eliminating oil-cans from the harderalloy metallic sheet-material: the combination with means for supporting the sheet in an attitude in which the faces of the oil-can are accessible in a direction perpendicularly to the faces; of first and second coaxial, and opposedly separated clamping members movable relatively to each other to clamp the peripheral portion of said oil-can substantially immobile in said attitude; heating means carried by at least one of said movable members for applying a predetermined heating to said oil-can while same is clamped as aforesaid; first and second metal shrinking dies respectively mounted within the confines of the first and second clamping members; the first die being movable inside the first clamping member and having a warped metal-working surface, the second die having a substantially planar surface confronting said warped surface and serving as an anvil whereby movement of the first die urges the metal of the oil-can radially outwardly away from the center thereof in a direction opposed to the direction of the residual stresses in the oil-can, thereby to shrink and eliminate the oil-can.

5. Apparatus for eliminating oil-cans from metallic sheet-material, comprising: means for supporting metallic sheet-material with the oil-can in an accessible attitude; means movable rectangularly toward the supported oil can, said movable means and said supporting means including opposed, complementary portions for applying a clamping action to said oil can substantially peripherally thereof upon further movement of said movable means; means for heating the clamped oil-can to a predetermined temperature; first and second dies mounted coaxially in spaced alignment in the apparatus, the first die being vertically movable and the second die being fixed and immobile, said dies having mutually confronting surfaces shaped with reference to each other and to the shape of the oil-can that movement of the first die toward the second die bodily urges the metal of the oil-can radially outwardly toward the periphery of the oil-can; and means for moving the first die toward the second die until the oil-can is flattened against the second die thereby to shrink and eliminate said oil-can.

6. Apparatus for eliminating oil-cans from metallic sheet-material, comprising: a frame; means in the frame for supporting the sheet with the oil-can accessible rectangularly thereto; two-phase ram means movable coaxially toward said supported oil can to clamp same peripherally with the supporting means in a first phase of movement of the ram means; and a pair of mutually coaxial metal-working die means disposed in said ram means and in said supporting means and mutually shaped and arranged to apply a metal-shrinking action the oil can in the second phase of said ram so as to neutralize the radially directed forces in said oil-can.

7. Apparatus according to claim 6 and in which said ram means consists of a columnar element movable vertically upwardly and downwardly in said frame with reference to said supporting means, said columnar element having a lower portion vertically divided into two coaxial segments mutually spaced apart, the upper segment being fixed to the lower end of the columnar element and the lower segment terminating at its lower end interposed coaxially between the two segments and en abling upward resilient yielding of said second segment upon application to said ram means of the second-phase actuating force.

8. An apparatus according to claim 6 and in which said pair of dies consists of a convex-faced die mounted coaxially in the lower end-portion of said ram means and a plane-faced die mounted coaxially in said supporting means with the plane-face confronting the convex face, whereby to enable said apparatus to shrink out of said sheet, oil cans therein that protrude upwardly from said sheet.

9. An apparatus according to claim 6 and in which said pair of dies consists of a first concave-faced die mounted coaxially in the lower end portion of said ram means and a second plane-faced die mounted coaxially in said supporting means, the ram means and the supporting means being arranged coaxially with the plane-face of said second die confronting the concave face of said first die, whereby to enable said apparatus to shrink out of said sheet oil cans therein.

10. Apparatus for eliminating an oil-can in a metallic sheet of material, comprising: means for supporting said sheet in a press-like apparatus with the sheet in an attitude in which both faces of the oil-can are accessible to forces directed normal thereto; means for clamping the peripheral marginal portion of the oil-can in a substantially immobilized condition leaving the oil-can free of said clamping means; movable die means and fixed die means arranged coaxially inside said clamping means, said die means being predeterminedly mutually shaped with respect to each other and to the oil-can for forceful contact of the dies with the oil-can to compressively urge metal away from the center and to the periphery of the oil-can; and means for moving the movable one of said dies to flatten the oil-can into permanent coplanarity with the remainder of the sheet.

11. Apparatus for eliminating an oil-can from a metallic sheet of material, comprising: means for supporting said sheet in a press-like apparatus with the sheet in an attitude in which both faces of the oil-can are accessible to forces directed normal thereto; means for applying to the periphery of the oil-can an oil-can segregating clamping action and sheet immobilizing action; means for heating the oilcan in the area inside the clamped periphery thereof; and compression exerting means for shrinkingly urging the metal in the oil-can that lies in the area inside the clamped periphery radially outwardly from the central region of the oil-can toward its periphery thereof, the so urged metal neutralizing the radially inwardly directed residual stresses in the sheet that gave rise to the oil-can.

12. Means for eliminating the oil-can from a metallic sheet, comprising: means for supporting said sheet in an attitude that exposes both faces of the oil-can to forces directed normal thereto; means for clamping the periphery of the oil-can in a stationary condition; means for heating only that portion of the oil-can that lies within its clamped periphery; and fixed and movable die means for applying, in a direction normal to the faces of the oil-can, compressive forces having components urging the metal in the central region of the oil-can radially outwardly toward the periphery thereof so as to shrink and eliminate the oilcan.

References Cited in the file of this patent UNITED STATES PATENTS 438,408 Dewey Oct. 14, 1890 1,809,168 Junkers June 9, 1931 1,960,000 Chesney May 22, 1934 2,010,996 Junkers Aug. 13, 1935 2,112,653 MacLennan Mar. 29, 1938 2,350,884 Ernst June 6, 1944 2,439,571 Julian Apr. 13, 1948 2,693,638 Anderson Nov. 9, 1954 2,783,363 Gunther Feb. 26, 1957 

1. A METHOD OF ELIMINATING AN OIL-CAN IN METALLIC SHEETMATERIAL, COMPRISING: SUPPORTING SAID SHEET IN AN OPERATIONS ZONE IN AN ATTITUDE IN WHICH BOTH FACES OF THE OILCAN ARE RECTANGULARLY ACCESSIBLE; CLAMPING THE PERIPHERAL MARGINAL PORTION OF THE OIL-CAN IN A SUBSTANTIALLY IMMOBILE CONDITION, LEAVING THE REMAINDER OF THE OIL CAN RELATIVELY MOBILE; HEATING THE OIL-CAN WHILE THE MARGINAL PERIPHERY THEREOF IS CLAMPED; AND BALANCEDLY APPLYING TO THE AREA OF THE OIL-CAN THAT LIES RADIALLY INWARDLY OF THE AFORESAID CLAMPED PORTION A COMPRESSION FORCE DIRECTED RECTANGULARLY TO THE FACES OF THE SHEET AND OF SUCH MAGNITUDE AS TO PRODUCE AN EFFECTIVE RESULTANT VECTOR DIRECTED RADIALLY OUTWARDLY AND DOWNWARDLY WITH RESPECT TO THE RADIALLY INWARDLY ACTING RESIDUAL FORCES CAUSING THE OIL CAN. 